The world champion, who has a 17-point lead over Vettel after five races, made a few errors that compromised his overall lap time.

But there will be questions as to whether Mercedes are struggling in Monaco for the second year in succession after he said over the radio that something did not feel right while he was doing a race-simulation run on the super-soft tyre, the hardest of the three compounds available this weekend.

Running in race trim on the hyper-soft, Vettel appeared to have a pace advantage over Hamilton of about 0.3secs, although practice times are not always an accurate measure of actual form.

"It was a decent day," said Vettel. "I am not that happy yet in the second and last sector. I trust in the car so I can play around but I am sliding a bit too much so I think there is something we can do better.

"I don't think we got the best out of the tyres when we were running due to traffic. For Saturday it will be very close."

Verstappen appeared to have the advantage in second practice until Ricciardo edged clear as he strung together a series of laps on the hyper-softs a little later than Verstappen's run.

Red Bull have flattered to deceive in practice a number of times already this season, but there are signs that this weekend might be different.

Ricciardo famously lost victory in Monaco in 2016 when he was leading comfortably only for his team to fail to have his tyres ready at a pit stop, handing the lead to Hamilton.

Ricciardo said this week that he felt Monaco still owed him a win, but added: "I've got to go and earn it. It's not going to happen without me putting the effort in. Maybe some circumstances will help me out but for sure I've still got to be prepared to put the effort in."

Renault's Nico Hulkenberg was seventh fastest, ahead of the McLarens of Stoffel Vandoorne and Fernando Alonso, the latter's day compromised slightly by losing most of the first session because of a brake-by-wire issue.

Haas, who impressed at the last race in Spain with Kevin Magnussen finishing sixth, well clear of the other midfield runners, appeared to be struggling, the Dane 16th with team-mate Romain Grosjean two places further back.

There was only 0.5secs between Hulkenberg in seventh and Sauber's Charles Leclerc in 17th.

Behind the scenes, Ferrari are the subject of an investigation into the operation of the energy store in their hybrid system by governing body the FIA, who are concerned that it could be used in an unscrupulous way.

Despite its concerns, the FIA has no evidence it has been used in such a manner and insiders say the FIA, after an inquiry lasting more than a month, is moving towards a position where it is satisfied there is no chance the energy store can be used in a way it should not be.

And Vettel appeared unfazed by the episode when questioned after second practice.

"We heard about it but it is normal that every now and again you have something popping up and then there's rumours," he said.

"This time it's us. In four weeks' time probably someone else. Ultimately it is the FIA's job to look after everyone and we trust them as much as the other teams do to do their job."

Red Bull have dominated the weekend so far and looked set to lock out the front row until Verstappen's costly error in final practice.

The Dutchman caught the inside wall at the second Swimming Pool chicane with his right front tyre and catapulted into the barriers on the outside.

Verstappen's car was badly damaged in the FP3 accident
The impact damaged both front and rear suspension on the right-hand side of the car and the damage was too extensive to be fixed in the two hours and 15 minutes between the end of practice and when he would have needed to get out to do a lap in first qualifying.

To add insult to injury, Verstappen has a five-place grid penalty for an unauthorised gearbox change because the team discovered a leak from a crack in the gearbox as they were preparing the car for qualifying, but it is academic as he will start from the back anyway.

What they saidRicciardo: "We didn't change much on the car this weekend. I have just been able to build up to it and have some fun. I love this race and it's a pleasure to drive. It has been awesome."

On Verstappen's incident: "To be fast you can't think about those things. We need to push it but you don't need to over-drive it. We are both pushing each other and it is no surprise these things can happen, When you're lapping 1:10s, 1:11s, there is no room for error."

Vettel: "I was pretty happy. There is always the feeling there is a little bit [more]. I don't think I could have threatened Daniel's time today.

"Well done to Daniel, he owned the qualifying session, we were playing around with the set-up quite a bit to squeeze everything out. We have put ourselves in a good position, we put ourselves as close as well could and we see what we can do in the race."

Hamilton: "We knew we weren't as quick as him [Ricciardo]. We did the best we could and the car was in a good place. My last lap, I was up 0.27secs [after the first sector] but I lost it in the middle and last sector, so naturally not happy with that. That wouldn't have been enough anyways for pole but it would have made a difference, obviously I would have been second. You can't always get it perfect and I live to fight another day."

The battle behind the big six
Ocon impressed in emerging as best of the rest, pipping McLaren's Fernando Alonso by just 0.049secs.

Alonso was just 0.02secs ahead of Renault's Carlos Sainz, who beat team-mate Nico Hulkenberg, in 11th, on merit in qualifying for the first time since joining Renault for the last four races of last season.

The second Force India of Sergio Perez and Toro Rosso's Pierre Gasly completed the top 10.

Taking the plunge: Ricciardo celebrates in style with a theatrical dive into the rooftop swimming pool at Red Bull's hospitality unitRedemption for Ricciardo
Ricciardo had said in the build-up to the race that he felt Monaco owed him a win, following the pit-stop bungle that cost him victory in 2016, but admitted he would have to "earn it".

His words turned out truer than he could have imagined at the time, as a race that had looked to be turning into a relatively easy cruise suddenly became filled with jeopardy.

"Two years later I finally feel like redemption has arrived," Ricciardo said.

"We had a lot to deal with during the race. I felt loss of power and I thought the race was done. I got home just using six gears. Thanks to the team I got it back.

"There were a few doubts getting it to the end of the race but we won Monaco."

As if nursing a poorly car to victory was not enough, Ricciardo even managed to persuade Princess Charlene of Monaco to drink some bubbly on the podium
Ricciardo led away from pole, fending off the faster-starting Vettel, and controlled the opening part of the race, making his first pit stop on lap 17, to cover the German's stop a lap before.

With all drivers managing their tyres, and lapping seconds off the limit to ensure they needed to do only one stop, the race seemed already settled.

But then Ricciardo came on the radio complaining of a lack of power. The team said they could see what the problem was - but did not say to avoid rivals finding out - and told him it would not improve.

It turns out he lost the MGU-K - the part of the hybrid system that recovers energy from the rear axle and redeploys it. Team boss Christian Horner said it cost him 2.5 seconds a lap and 25% of engine power, or about 225bhp.

Ricciardo had held a three-second lead after the pit stops, but now had Vettel right behind him and knew he faced a difficult, exhausting race managing the engine problem while ensuring the German did not get close enough to try a pass.

He was helped by the arguably ridiculous situation of drivers lapping four or five seconds off their potential maximum pace to ensure their tyres lasted.

This was the case throughout the race, whether drivers were on the fragile hyper-soft qualifying tyres, or on the two harder options, the super-soft and ultra-soft.

As such, the race provided uncomfortable memories of the first six years of Pirelli's tenure in F1, before it was asked to provide more raceable tyres to enable drivers to push harder in the faster, more demanding cars that were introduced in 2018.

Ricciardo was one of the drivers centrally involved in forcing that to happen, but he will not care about it right now, after finally taking a well-deserved and overdue win at the most prestigious event of the year.

"I don't know how you did that," engineer Simon Rennie said to Ricciardo in congratulating him over the radio on the slowing-down lap.

Sebastian Vettel was never far from the rear win of Daniel Ricciardo's car throughout the race, but was unable to find a way past
Horner said: "You have done an amazing job today. That is right up there with what Schumacher did... and it is payback for 2016."

Horner was referring to Michael Schumacher's drive in the 1994 Spanish Grand Prix, when the German finished second for Benetton with only fifth gear.

Vettel, knowing overtaking was all but impossible, followed in his former Red Bull team-mate's wheel tracks until dropping back in the final five laps or so when his tyres ran out of grip.

Hamilton, who for a time was wrongly concerned the ultra-soft tyres fitted at his pit stop would not make the end, will probably look at the race as relatively successful damage limitation on a weekend Mercedes always expected to be difficult.

The second Ferrari and Mercedes of Kimi Raikkonen and Valtteri Bottas took fourth and fifth.

Up there with Schuey? Red Bull team boss Christian Horner appeared to draw parallels between Ricciardo's drive and Michael Schumacher's second place at the 1994 Spanish GPAlonso's first retirement
Best of the rest was Force India's Esteban Ocon, converting an excellent sixth on the grid into the same place as the finish but at the same demonstrating the extent of pace management at the front by moving on to the tail of Bottas' Mercedes in the closing laps.

Toro Rosso's Pierre Gasly benefited from McLaren driver Fernando Alonso's first retirement of the season with a broken gearbox to take seventh.

The Frenchman, who did a remarkable 37-lap stint on the hyper-soft tyres at the start of the race, had to fend off the Renault of Nico Hulkenberg and Red Bull's Max Verstappen to the end.

Verstappen drove a well-judged race to recover from his back of the grid start after a crash in practice caused him to miss qualifying. The Dutchman made a series of overtakes and balanced aggression with caution in a way he has struggled to do on so many occasions so far in his incident-strewn season.

With six laps to go, Sauber's Charles Leclerc, running 15th, smashed into the back of Brendon Hartley's Toro Rosso at the chicane when he suffered a brake failure, bringing out the virtual safety car, but it changed nothing about the result.

Driver of the day
Only one choice this time - Ricciardo utterly owned the weekend, fastest in all practice and qualifying sessions and leading the entire race.What's next?
Canada - and a race very different from Monaco. Another street circuit, but a fast one, where Hamilton excels, racing is furious, overtaking common and where both Renault and Honda have major engine upgrades of which much are expected. If Renault's lives up to expectations, Ricciardo could conceivably become a major title contender.

Ricciardo becomes just the third Australian to win the Monaco Grand Prix, after Mark Webber (2010, 2012) and Jack Brabham (1959, pictured)
Ferrari's Sebastian Vettel said of Ricciardo: "He was quicker than us, he was able to open a gap and I was never really a threat to him"
Third-placed Lewis Hamilton was not impressed with the race: "I will be shocked if anyone was awake at home while it was on, because I would have been asleep on the couch"
Sauber's promising rookie Charles Leclerc, a Monaco native, retired from the race after losing his brakes and was clearly disappointed: "It is just a shame because it happened at my home race"
Force India's Esteban Ocon, who finished sixth, was delighted with his performance: "When your engineer is telling you you are quickest on the track, it is probably the first time it happened this season!"